Optical communication systems are used to transmit information signals over optical fibers or waveguides. In order to increase the capacity of these systems, wavelength division multiplexing (WDM) is used to transmit multiple signals at different wavelengths over a single waveguide. A waveguide grating router laser (WGRL)such as disclosed in U.S. Pat. No. 5,373,517 entitled "Rapidly Tunable Integrated Laser" issued to Dragone et al., can be used as a multiple wavelength source for high performance WDM local access networks. The WGRL can simultaneously transmit N equally spaced WDM channels, each modulated with an information signal. The WGRL includes N separately addressable gain sections and an integral 1.times.N waveguide grating router (WGR) preferably integrated on a semiconductor wafer.
When A WDM local access network includes feeder fiber(s) from a central office to a remote node consisting of a waveguide-grating router (WGR), which is in turn connected to remote terminals (or optical network units) via multiple distribution fibers, the local access network is referred to as a WGR-based WDM passive optical network. By matching the wavelengths of the WGRL transmitter, located at the central office, to the WGR at the remote node, distinct broadband signals modulating each wavelength can be transmitted to each of N remote terminals.
WGR-based WDM passive optical networks are thus well suited to transmit distinct broadband signals to each of a multiplicity of terminals or subscribers (thereby establishing broadband point-to-point connections). However these networks are not optimized for the simultaneous transmission of broadcast signals, such as video, to all subscribers. A passive splitter based network can be used in addition to a WGR-based WDM passive optical network to transmit these broadcast signals. However, a drawback associated with this approach is that it requires a separate network to transmit the broadcast signals thereby requiring increased cost and complexity.
Another approach is to take advantage of spectral slicing through the WGR at the remote node to provide broadcast video signals without altering the outside fiber plant. Spectral slicing refers to a technique known in the art, whereby a light source (such as an LED), having a broad spectral output, is employed in conjunction with a WDM demultiplexer (or WGR demultiplexer) to generate a multiplicity of spectral bands. Thus, in the case of a WGR-based passive optical network, a single broadband source is modulated with broadcast information. The WGR at the remote node slices this broad spectrum and directs an equal fraction of the modulated optical spectrum to each subscriber. A disadvantage associated with this approach is that it requires an additional light source at the central office which increases the optical bandwidth of the system as well as requiring coarse WDM couplers at both the central office and at each subscriber's optical network unit.
Accordingly, there is a need for an optical network which simultaneously delivers both broadband and broadcast signals without requiring an additional overlayed network or an additional light source.